high-side switch
TomH
Posts: 3
Hello. When using a uC to switch power to a load, we normally can use an n-channel mosfet between the load and ground. But in some cases (servo, analog) the switch wants to be on the high side. Generally the load's supply voltage may be above the uC's. I am looking for recommendations for high-side switches. The simplest home-made version is an nmos driving a 10k resistor which drives a pmos. We do this all the time, but we'd love to find these three components in a single 3-pin 0.1" package that is as easy to use as an NMOS. Beyond that, there are high-side switch devices for sale which have many more pins and offer many unnecessary features (thermal shutdown, adjustable current limit, n-channel with Vgs charge pump) and are hard to find in a breadboardable package.
My dream part looks like: 3 pins (enable, vcc = 3-24V, and gnd); TO-220 or other 0.1"-pitch through-hole; enable logic threshold 1 or 2 volts; R_on < 0.1 ohm; Imax = 3 or 4 A.
We want to have tons of these in a handy bin for frequent use in prototypes or production.
How do others do this? Thanks in advance!
My dream part looks like: 3 pins (enable, vcc = 3-24V, and gnd); TO-220 or other 0.1"-pitch through-hole; enable logic threshold 1 or 2 volts; R_on < 0.1 ohm; Imax = 3 or 4 A.
We want to have tons of these in a handy bin for frequent use in prototypes or production.
How do others do this? Thanks in advance!
Comments
Now, having said that, you could make Vdd and V+ common, leaving V- several volts below Gnd. In this case a simple P-channel MOSFET will do the trick.
-Phil
-Phil
P.S. Caring for a six-month-old and merely dazed? I'd be catatonic!
Another option is a small opto-relay, such as:
http://www.irf.com/product-info/datasheets/data/pvdz172.pdf
That particular one comes in a 4 pin DIP8 package and is rated for up to 1.5 amp.
It has the advantage that the output is highly isolated (4000 volts) from the input, and it can switch up to 60 volts. A disadvantage is that the driver has to supply around 10 ma for the input LED to turn on the HEXFET.
A third option is a low dropout voltage regulator with a shutdown input.
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Tracy Allen
www.emesystems.com
The VR option is a good one — especially with an adjustable regulator like the LM2941. You can just ground the feedback pin and have it fully on or fully off, depending on the enable input. Plus you get many of the protections available in the BTS409 at a reduced cost:
····BTS409: 2.3A switching, $172.00/C
····LM2941: 1.0A switching, $99.70/C
Both come in a TO220-5 which, although it's a throughhole part, is hard to breadboard since the pins are so close together.
I've used the PVDZ172s in products before. They're quite nice, and the DIP is easy to breadboard, but you pay for the isolation: $526.92/C from DigiKey.
-Phil